Inhibitory effect of Zn²⁺ in zinc‐containing β‐tricalcium phosphate on resorbing activity of mature osteoclasts

Abstract

Long term effect of the growing instability of the bone-implant interface due to bone resorption at the interface is a problem for the implants, including bioactive ceramics. Zn2+ -containing tricalcium phosphate (ZnTCP) is a material which may overcome this problem. The present study aims to clarify whether Zn2+ -containing tricalcium phosphate (ZnTCP) ceramics with a Zn2+ content of 0.316 (ZnTCP316) and 0.633 (ZnTCP633) wt % suppress resorption by mature osteoclasts in vitro. Suppression would be due to an increase in the number of apoptotic osteoclasts and the inhibition of the resorbing activity of osteoclasts, the latter being the major mechanism of the suppression. The number of apoptotic osteoclasts was significantly 6.3 times higher with ZnTCP633 than with tricalcium phosphate ceramic (TCP) after 24-h culture. The net contribution to resorption of this change in apoptotic cell numbers is much smaller than that of the change in resorbing activity. The osteoclasts cultured on ZnTCP formed fewer actin rings than those cultured on the TCP. The mRNA expression of CAII and cathepsin K/OC2 in the osteoclasts on ZnTCP633 was downregulated 0.5-fold and 0.6-fold, respectively, compared with that on the TCP. The volume of resorption pits was downregulated 0.4-fold in the ZnTCP633 than that in TCP. These results suggest that ZnTCPs suppressed the resorbing activity of mature osteoclasts probably through a local increase in the level of Zn2+. Bone substitutes or coating layers containing ZnTCP would be promising biomaterials from the viewpoint of counteracting osteoclastic bone resorption at the bone-implant interface.

Effect of titanium particles on osteoclast activity in vitro

“…osteoclast bone resorption is caused mainly by acid and lysosomal proteases, which are released through the ruffled border area into the space between the cell membrane and extracellular bone matrix. cat K, a lysosomal protease, is highly expressed in osteoclasts to degrade the organic matrix (26)(27)(28). in this study, titanium particles at a lower concentration slightly enhanced the mrna expression of cat K, which was probably due to the reaction of osteoclasts after the phagocytosis of titanium particles.…”

Interlaboratory studies on in vitro test methods for estimating in vivo resorption of calcium phosphate ceramics

“…7) do not take account of material-mediated differences in the total number of pits or osteoclasts between TCP90, 0.5ZnTCP and 1.0 ZnTCP. The number of resorbing osteoclasts slightly decreases with an increase in the zinc content of TCP in vitro [32]. Thus, the relative dissolution rates multiplied by the total number of osteoclasts or resorption pits would be better correlated to the relative amount of osteoclastic resorption in vitro.…”

“…Previous data of volume of osteoclastic resorption pits measured at research center A on the TCP90, 0.5ZnTCP and 1.0ZnTCP disks (Specimens 13-15, respectively) with relative densities of 91-93% was analyzed -The previous paper reported incorrect relative densities (67-83%) for the disks - [32]. Briefly, the osteoclasts were isolated from unfractionated bone cells in the bone of 10-day-old Japanese white rabbits.…”

Historical Review of Biological Apatite Crystallography

“…Zinc and/or magnesium containing calcium phosphate [119][120][121][122][123] , and the osteoconductive calcium phosphates [124][125][126][127][128] have been studied and applied to clinical uses.…”